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good read about 64bit DDR vs 128bit SDR RAM

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  • good read about 64bit DDR vs 128bit SDR RAM

    http://www.digit-life.com/
    Thats where it came from.

    This is the main bit, for those of you who are interested.

    Oh, its about the MX, but interesting anyway.


    With the GeForce2 MX however we are looking at a different market segment. These people are those who are not on the cutting edge of the performance curve and demand value for money over performance. For that reason their machines will have a much lower specification. So in their case there is every possibility that they will be CPU limited ... in this case the memory bandwidth is irrelevant.

    Faster is not necessarily faster!

    Looking at the figures you would assume that because the memory is faster then obviously the card is faster in situations where memory bandwidth is involved. Confusingly this is not necessarily the case. On a 128-bit architecture you take information from memory 128 bits at a time regardless of how much information you actually want. Suppose for example you only want 40 bits of information .. you still have to take 128-bits. So the
    question is how many of the additional 88-bits are utilized? The answer varies hugely from one application to another but on average one is lucky to get 70% utilization. So for every 128-bits read from memory 26-bits are useless.

    Now lets compare this to 64-bit architecture where we read 64-bits at a time ... here there are only 24-bits that are additional to our requirement. So if we again assume that we have a 70% utilization then in this case 7-bits are useless. On the DDR we read memory twice as fast so for the same 128-bit access we have a redundancy of only 14-bits (compared to 26 bits on SDR). In summary, because the memory is more efficient it appears faster, and as a result the apparent slowness of the memory clock is not a factor.

    So which is faster?

    The honest answer to this is that they are about the same. In some applications DDR will be faster and in some applications the SDR will be faster. There is also an issue of overclocking where I believe that the DDR will have more headroom and should produce faster results.

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